Steel making apparatus

ABSTRACT

An apparatus for making lead-bearing steel which comprises a melting furnace, and a ladle for receiving a stream of molten steel discharging from said melting furnace and spaced therefrom. The lead is fed to the stream of molten steel at a point where the latter is being poured from the melting furnace to the ladle. The latter has an interior bottom surface and a ladle outlet adjacent thereto. The ladle outlet prevents substantially any lead deposited on the interior bottom surface of the ladle from being discharged from the ladle, when the latter is poured or tapped.

United States Patent 91 Ormaechea 1 June 4, 1974 1 STEEL MAKING APPARATUS [76] Inventor: Jose Joaquin Aguirre Ormaechea,

lndependencia 1,, Vitoria, Spain [22] Filed: Nov. 8, 1971 [21] Appl. No.: 196,607

Related US. Application Data [62] Division of Ser. No. 79,529, Oct. 9, 1970, Pat. No.

[30] Foreign Application Priority Data 3,061,298 10/1962 YamaZOe 266/34 V 3,182,359 5/1965 Gero 266/34 T 3,193,892 7/1965 Sickbert 266/34 V 3,224,051 12/1965 Brown et a1 266/34 T 3,258,328 6/1966 0055 et a1. 75/57 3,671,224 6/1972 North et a1. 75/129 FOREIGN PATENTS OR APPLICATlONS 519,572 4/1940 Great Britain 75/123 F Primary ExaminerGerald A. Dost [57] ABSTRACT stantially any lead deposited on the interior bottomsurface of the ladle from being discharged from the ladle, when the latter is poured or tapped.

3 Claims, 3 Drawing Figures PATENTEDJUH 4 I974 SHEET 3 OF 3 PIC-5.3

1 STEEL MAKING APPARATUS This is a division of the copending patent application Ser. No. 79,529, filed October 9, 1970 which issued on Sept. 4, 1973 into U.S. Pat. No. 3,756,805.

The present invention relates to an apparatus for treating molten metal.

As is well known, lead-bearing steels have a greater machinability, when worked on chip-producing machine-tools, than steels of the same basic composition that do not contain lead.

Known classical methods of producing lead-bearing steels are based upon the hitherto accepted supposition that lead is insoluble in steel.

in order to produce, by classical methods, leadbearing steels having an adequate degree of homogeneity, it has been thought necessary to add the lead in the form of granules, just before the steel solidifies, with the object of avoiding segregation of the lead due to gravity and as a result of the substantial difierence between the density of steel and of lead. Consequently, in the classical method, the granules of lead are added to the molten material at the moment at which it is poured into the mold.

It is an object of the present invention to provide an apparatus for making lead-bearing steel which is a melting furnace, a ladle for receiving a stream of molten steel discharging from the melting furnace and spaced therefrom. Lead is fed to the stream of molten steel at a point where the latter is being poured from the melting furnace to the ladle. The ladle has an interior bottom surface and a ladle outlet adjacent thereto, and at the ladle outlet it is provided for substantially preventing any lead deposited on the interior bottom surface of the ladle from being discharged from the ladle when the latter is poured or tapped.

With this and ot l ei' objectsljn view whicl v vill be- The ladle outlet 7 is more particularly disclosed in FIGS. 2 and 3. F IG. 2 shows an arrangement in which a base 8 of the ladle has a projecting portion or upstanding rim 9, whereby it is raised above the opening of the ladle outlet. In FIG. 3 there is shown another arrangement in which a sleeve 7 defining the ladle outlet has one end thereof raised above the flat base 8 of the ladle. A plug 10 is provided for opening and closing the ladle outlet.

The process comprises adding solid or liquid lead to the stream of molten metal as the steel is poured from a melting fumace to a ladle. The lead is thus added under conditions in which the temperature and oxidation of the bath are controlled.

At the moment when the addition is made, the steelbath should exhibit a presence of reactive oxygen suffcient to permit the formation of lead-oxide, the vapour of which is soluble in the molten steel. The lead-oxide formed has a low boiling point and causes bubbling of the steel bath which becomes saturated with this compound.

The bubbling caused by the lead-oxide vapour which passes through the bath and saturates it, reduces the content of oxygen, hydrogen and other gases dissolved in the steel, and thus indirectly improves the quality of the steel.

The amount of reactive oxygen necessary for the formation of lead-oxide will depend upon the composition of the steel, and care is taken not to add aluminium to the bath before the lead has been added.

In the case of aluminium-killed steels, aluminium is added to the metal in the ladle in the final stages. This constitutes no drawback since it corresponds to normal manufacturing procedure.

Table No. 1 shows the solubility of lead-oxide as a function of the temperature of the bath, as established on the basis of numerous tests:

come apparent from the following detailed description, the present invention will be clearly understood in con- .nq tism. with an in drawing in which:

FIG. 1 is a schematic vertical longitudinal section through a melting furnace, a ladle and the means for adding the lead at the moment at which the metal is poured into the ladle and the addition of lead is made;

FIG. 2 is a schematic vertical longitudinal section through the ladle showing one construction thereof according to the present invention of the ladle outlet; and

The solubility of lead in steel is independent of the composition of the steel and is determined solely by temperature.

The temperature at which the metal is poured into the ladle should be greater than l,600C and is governed by the percentage of lead required in the steel, as shown in Table No. I.

As can be seen from the Table, when the temperature of the bath drops below l,600C, as occurs in most cases when the steel is still in the ladle, the solubility of the lead in the steel is practically zero. Under these conditions lead-oxide is precipitated in the form of a fine and homogeneous dispersion, the particles of which do not settle by means of gravity, so that the lead is homogeneously distributed after solidification has taken place.

The remainder of the lead, insoluble in the steel at the temperature at which the addition is made, forms relatively large droplets, which each settle by gravity over a period of time not greater than 5 minutes, and are deposited on the base of the ladle. Thus, after the lead has been added, a minimum period of about 5 minpreferably should be 40 percent greater than the quantity that it is desired to incorporate in the steel.

The lead is added at the feed point via means 4 (FIG. 1) at a rate equal to that required at the upper part 6 of the stream of molten steel.

The rate of supply of the lead needed at the feed point 4 in FIG. 1 can be determined by simple tests, the aim being to have a supply of solid or liquid lead reaching the stream of molten metal during practically the entire period during'which pouring takes place. Nevertheless, the system does not call for a high degree of coordination in this operation, since, as previously indicated, if too much lead is added this does not become incorporated in the bath but is deposited on the base of the ladle. v

The method does not require any high capital cost equipment. The only requirement is that of positioning the ladle outlet 7 or a rim 9 in such a way that it projects upwards of or beyond the plane of the base 8 of the ladle 3, thus preventing the lead, deposited on the base, from being entrained by the stream of steel which emerges through the mouth piece 7 when casting takes place.

Despite the above-mentioned precautions, a small quantity of lead may be deposited directly on the surface of the ladle outlet. This lead can be eliminated simply by slight purging of the steel prior to casting it in the mold.

The method can be applied to all kinds of steel compositions and can be adopted in present-day steelproducing techniques.

The method can be used in all the usual steel-making processes, for example, Siemens-Martin, electric fur nace, L. D., continuous casting, or mold-casting by the siphon or direct methods.

These improvements result in advantages regarding an even and finely-dispersed distribution of the lead both at the top and the bottom of the ingot. Similarly,

segregations do not occur either on the surface or in the middle of the ingot.

Consequently, ingots manufactured by the method do not need to be end-cropped, as is the case with in-.

gots manufactured by the classical methods. In this connection, experience from numerous casting operations has shown that with the method an output can be obtained that is of the same order of magnitude as that obtained with steels of an identical basic composition, but containing no lead.

The lead particles form a fine, homogeneous dispersion, the grain-size'of which is often less than. one micron.

Tests carried out so far using the stated method show that this particular method for the addition of lead has no adverse effect upon the fatigue behavior of the steel or upon its mechanical properties.

While I have disclosed one example of the present invention, it is to be understood that this example is given by illustration only and not in a limiting sense.

We claim:

1. An apparatus for making lead-bearing steel containing a uniform distribution of lead, comprising a melting furnace,

a ladle below said furnace for receiving a pouring stream of molten steel discharging from said melting furnace,

means for feeding lead directly into said pouring stream of molten steel at a. suspended transferring point where the latter is being poured out from said melting furnace to said ladle between the latter and the former,

said means including a duct having a discharge end extending above said ladle, said duct being downwardly inclined toward said stream whereby said 'lead is made to flow to said point by gravity,

means for controlling the temperature and oxidation of the bath jointly with the feeding of the lead to said molten steel,

said ladle having an interior bottomsurface and a ladle outlet adjacent thereto, and

barrier means at the ladle outlet for substantially preventing any lead deposited on said interior bottom surface of said ladle from being discharged from said ladle when the latter is poured or tapped.

2. The apparatus, as set forth in claim 1, wherein said ladle outlet means comprises an upstanding rim projecting upwardly from said interior bottom surface of said ladle.

3. The apparatus, as set forth in claim 1, wherein said ladle outlet means comprises a sleeve means having an upstanding portion projecting upwardly beyond said interior bottom surface of said ladle and constituting said ladle outlet. 

1. An apparatus for making lead-bearing steel containing a uniform distribution of lead, comprising a melting furnace, a ladle below said furnace for receiving a pouring stream of molten steel discharging from said melting furnace, means for feeding lead directly into said pouring stream of molten steel at a suspended transferring point where the latter is being poured out from said melting furnace to said ladle between the latter and the former, said means including a duct having a discharge end extending above said ladle, said duct being downwardly inclined toward said stream whereby said lead is made to flow to said point by gravity, means for controlling the temperature and oxidation of the bath jointly with the feeding of the lead to said molten steel, said ladle having an interior bottom surface and a ladle outlet adjacent thereto, and barrier means at the ladle outlet for substantially preventing any lead deposited on said interior bottom surface of said ladle from being discharged from said ladle when the latter is poured or tapped.
 2. The apparatus, as set forth in claim 1, wherein said ladle outlet means comprises an upstanding rim projecting upwardly from said interior bottom surface of said ladle.
 3. The apparatus, as set forth in claim 1, wherein said ladle outlet means comprises a sleeve means having an upstanding portion projecting upwardly beyond said interior bottom surface of said ladle and constituting said ladle outlet. 